1. Field of the Invention
The present invention relates to a zoom lens system and an electronic image pickup apparatus using the same.
2. Description of the Related Art
In recent years, instead of a silver halide film camera, a digital camera has been a mainstream which photographs a subject by use of a solid-state image pickup device such as a CCD image sensor or a CMOS type image sensor. Furthermore, the camera has a large number of categories in a broad range from a highly functional type for business to a compact popular type. In the present invention, the category of the compact popular type is especially noted.
A user of such a popular type of digital camera would like to readily enjoy photographing in a broad scene anywhere and anytime. Therefore, the user would like a small-sized camera, especially a digital camera of a thin type which is conveniently carried with a good storage property in clothing and bag pockets and which has a small size in a thickness direction.
On the other hand, a zoom ratio of the digital camera of a compact type has been generally about three, but there is a further demand for a camera having a zoom ratio higher than that of a conventional camera in order to broaden a photographing area.
As a compact zoom lens system having a comparatively high zoom ratio, a type is known which has, in order from an object side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power and a fourth lens unit having a positive refractive power (e.g., see Japanese Patent Application Laid-Open Nos. 2001-133687 and 11-119100).